Update statement with FROM clause with multi joins

Question

0.00/5 (No votes)

See more:

how the sql Update statement work , while using FROM Clause with multiple joins[also in this situation how the WHERE clause work] ?,

also is it necessary that the table which is getting updated has to be in FROM clause ?

kindly explain

Posted 3-Sep-13 5:21am

anbujeremiah

Add a Solution

2 solutions

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

ZurdoDev · Answer 1 · 2013-09-03T06:01:00

Solution 1

Update works on the table you tell it to. For example:

SQL

UPDATE table1 
SET Field1 = ''

will update table1.

The from clause will limit what gets updated. You don't need a From clause unless you are trying to join in other tables.

Posted 3-Sep-13 6:01am

ZurdoDev

Comments

anbujeremiah 3-Sep-13 20:18pm

so FROM clause will act as WHERE clause ?

ZurdoDev 3-Sep-13 20:47pm

No. You could do, for example

UPDATE table1
SET Field1 = ''
FROM table1 t1
INNER JOIN table2 t2 ON t1.CustomerID = t2.CustomerID
WHERE t2.City = ''

This will update Table1.Field1 to a blank where the corresponding record in Table2 has a blank City. You really only need from when you are joining in another table.

Or, you could do something like this:
UPDATE Table1
SET Field1 = ''
WHERE Field1 IS NULL

So, if Field1 is null it will get changed to a blank.

anbujeremiah · Answer 2 · 2013-09-15T13:49:00

Solution 2

also is it necessary that the table which is getting updated has to be in FROM clause ?

Posted 15-Sep-13 13:49pm

anbujeremiah

Comments

Zerotimedev 15-Sep-13 22:58pm

i think from the tests i tried it needs to be set as the 'from' table to update. If you needed to reference another table then you would inner join to that, otherwise if you need to update 2 tables you will probably just need a second update query.